In some semiconductor process chambers, multiple process gases can be delivered to the process chamber through a common gas inlet, for example, a gas injection funnel disposed in the ceiling of a process chamber. Such semiconductor process chambers may include those used for chemical vapor deposition (CVD) or atomic layer deposition (ALD) wherein the process gases may be utilized to at least partially deposit a layer on a substrate.
The volume of a common gas inlet can be substantially greater than the volume of a gas conduit which supplies a process gas to the inlet. Consequently, the process gas rapidly expands when entering the inlet. The rapid expansion of the process gas can result in cooling of the process gas—an effect known as Joule-Thompson Cooling. Process gases having low vapor pressures, for example hafnium tetrachloride (HfCl4), will condense upon cooling, thus forming particles that may contaminate the inlet or result in concentration variation in the process gas.
Further, tangential alignment of a gas conduit relative to a central axis of the common gas inlet can result in a circulating gas vortex in the gas inlet and over the substrate. The vortex can cause the process gas, for example, comprising a carrier gas and a reactant vapor, to become separated resulting in concentration variations in the process gas.
Accordingly, there is a need in the art for a gas delivery assembly that prevents rapid cooling and vortex formation.